The present invention relates to mechanically operable acoustic filters for varying the acoustic spectrum of sound signals transmitted. Such a filter is adapted for use in acoustic devices or instruments, namely stethoscopes.
Among present-day acoustic filters two types may be discerned:
(1) FILTERS UTILIZING ELECTRONIC AMPLIFIERS IN WHICH THE SIGNALS ARE MODIFIED AND FILTERED, AS DESIRED, BY ELECTRONIC MEANS AND THEN RECONVERTED INTO SOUND WAVES;
(2) OTHER FILTERS IN WHICH THE SOUND WAVES CANNOT BE FILTERED VARIABLY AND CONTINUOUSLY.
A stethoscope is known having two chest pieces one of which is an open, filterless chest piece and the other chest piece is fitted with a rigid diaphragm which is applied against the patient's skin in use. The amount of filtering produced by such a stethoscope is fixed and the filter member (i.e. the diaphragm) acts positively and directly on the sound source by its contact with the skin of the patient.
There are other known stethoscopes having a single chest piece which are provided with a diaphragm against which a smaller diameter annular member is applied to achieve two fixed filter settings and others with a diaphragm which, depending on the pressure with which its applied against the patient's skin modify the response curve of the transmitted sound waves.
Non-electrical devices are also known in which (1) the response curve is fixed; (2) if it is not fixed it is obtained by varying the pressure exerted on the skin which makes their use inconvenient and their results inaccurate; and (3) the variation of the response curve is effected by contact of the diaphragm with the patient's skin and not by acting directly on sound waves transmitted through a gaseous medium, which limits their use to medical stethoscopes.